Method for hard surfacing tools



March 30, 1965 Filed Dec. 1, 1960 H. C. BRIDWELL ETAL METHOD FOR HARD SURFACING TOOLS 3 Sheets-Sheet 1 Harold C. Bridwell David S. Rowley By %WA 2. QM-L.

Inventors Attorney March 30, 1965 H. c. BRIDWELL. ETAL 3,175,427

METHOD FOR HARD SURFACING TOOLS Filed Dec. 1, 1960 3 Sheets-Sheet 2 Harold C. Bridwell David S. Rowley Inventors By %wt. QLLL Attorney March 30, 1965 H. c. BRIDWELL ETAL 3,175,427

METHOD FOR HARD SURFACING TOOLS 3 Sheets-Sheet 3 Filed Dec. 1, 1960 L E E T S STEEL MATRIX BOND FIG. IO

Harold C.'Bridwell David .S. Rowley lnveniors By W E. Q.....L Attorney United States Patent 3,175,427 METHGD FUR HARD fiURFAClNG TOQLS Harold C. llridwell and Bavid S. Roy/icy, Tulsa, 02th., assignors to Jersey Production Research Company, a corporation of Delaware Filed Dec. l, 1966, Ser. No. 73,619 7 Claims. (ill. 76-108) The present invention relates to rotary bits for drilling boreholes in the earth and more particularly relates to improved rotary drag bits useful for drilling oil wells, gas wells and similar boreholes. In still greater particularity, the invention relates to drag bits provided with improved blades which are able to withstand greater stresses than blades utilized in the past and to a method for fabricating such improved blades.

Except in certain areas where clays and similar materials prevent the efiicient use of roller cone bits, drag bits are not widely employed for drilling oil wells, gas wells and similar boreholes. The principal reason for this is the relatively short drilling life of the conventional drag bit. Such a bit can normally be used to drill only a few hundred feet of hole before it must be retipped or fitted with new blades. Trips into and out of the borehole must therefore be made at frequent intervals. Each such trip requires that the drill string be withdrawn from the borehole, that the pipe and drill collars be dismantled and racked, that the worn-out bit be replaced by a new one, and that the string then be reassembled and lowered back into the hole. A single trip usually requires several hours and is thus costly and time consuming. In order to minimize the number of trips which must be made and thereby keep down drilling costs drilling rig operators generally prefer to utilize roller cone bits wherever possible. Bits of the latter type can generally be used for longer periods than conventional drag bits and frequently permit higher drilling rates They are therefore usually less expensive than drag bits in terms of overall drilling costs.

There have been many suggestions in the past as to methods for improving the resistance of drag bit blades to wear and abrasion in order to increase drilling life and permit higher drilling rates. It has become conventional to employ large pads or inserts of tungsten carbide or a similar hard, abrasion-resistant material in such blades. Bits containing such pads or inserts usually perform much better than those provided with ordinary steel blades. Experience has indicated, however, that the increase in performance which can be obtained by this route is limited. Pads or inserts of tungsten carbide or the like which are bonded to a steel blade tend to fracture under the high blade stresses generated in moderately hard strata. To avoid this, it has been suggested that the tungsten carbide or similar hard metal be employed as small particles or chips and that these be supported in a matrix of softer material bonded to the leading edge of a steel supporting member by welding or infiltration. Blades provided with such chips generally wear better than those containing large inserts because the hard metal fractures are localized and do not usually extend through the matrix from one chip to another. The continual exposure of chips as the blade wears away results in the presentation of new cuttings edges to the formation and therefore permits higher drilling rates than can usually be obtained with blades having large inserts bonded directly to the blade body. Despite these advantages, the performance of such blades is often poor. It has been found that the matrix containing the chips frequently tends to split away from the blade body under high stresses, resulting in loss of the chips. This tendency limits the weight which can be applied to such bits and severely restricts their performance.

The present invention provides a new and improved drag bit blade which is relatively free of the difficulties which have restricted the effective utilization of rotary drag bits in the past. In accordance with the invention, it has now been found that drag bit blades prepared by using a molten matrix metal to infiltrate abrasion-resistant particles in contatct with a nickel-coated steel blade body are capable of withstanding greater stresses than blades available heretofore and, because of this increased stress resistance, have longer drilling lives and permit higher drilling rates than blades utilized in the past. The improved drilling life and higher drilling rates of the blade permit greater drilling footage per bit, reduce the number of trips which must be made into and out of the borehole in drilling to a given depth, and decrease the drilling time required. These factors result in lower overall drilling costs and may make drag bits competitive with roller cone bits in areas which were formerly considered unsuitable for drag bit operations.

The improved performance obtained with the drag bit blade of the invention can best be understood by first considering some of the stresses set up in a drag bit blade during a rotary drilling operation. The face or leading edge of such a blade normally has considerably higher resistance to Wear and abrasion than the steel which backs up and supports the leading edge. As a result, the leading edge usually extends slightly below the rest of the blade. A clearance angle is thus formed between the blade and the formation being drilled. Due to this clearance angle, longitudinal stresses at the bottom of the blade are much higher at the leading edge than at the trailing edge. High vertical compressive stresses are therefore set up in the matrix at the front of the blade; while the stresses in the steel body behind the matrix are appreciably lower. This leads to high shearing stresses across the bond between the matrix and steel. As the bit is rotated in contact with the formation, additional shearing stresses are generated due to longitudinal impact and uneven weight distribution on the several blades of the bit. Under these stresses, the bond between the matrix and steel frequently fails. A crack or fracture initiated in the bond at the point of contact between the blade and formation where stresses are greatest tends to act as a stress riser and hence the crack or fracture tends to advance up the blade. Large volumes of the matrix and the cutting elements contained therein may be lost from the face of the blade in a relatively short time. This reduces the resistance of the blade to Wear and abrasion and usually has a pronounced adverse effect upon drilling rate.

Metallurgical studies of the bonding in drag bit blades prepared by the infiltration technique have shown that susceptibility to failure at the matrix-steel bond under high stresses is often due to the presence of voids near the juncture between the steel and the matrix metal. These voids are too small to be seen with the naked eye and can only be detected under a microscope. The reasons for their existence are not wholly understood. It is believed, however, that the voids may result from oxidation of the steel to form iron oxide which in turn react with carbon dissolved in the matrix to produce minute quantities of carbon monoxide or carbon dioxide during the infiltration process. Other mechanisms may also be involved. Efforts to avoid formation of the voids by varying the blade fabrication technique, the matrix composition or the steel used have not met with success. Regardless of the materials and techniques applied heretofore, voids were generally present. It has now been found, however, that spch voids can be avoided by nickel-coating the steel body before the matrix is bonded to it by infiltration. The nickel apparently protects the steel against oxidation during the preliminary stages of the infiltration process and then goes into solution in the molten matrix adjacent the steel, promoting better wetting of the body by the matrix and a stronger bond than can otherwise be obtained. The finished blade is characterized by a higher nickel concentration in the immediate vicinity of the steel than elsewhere in the matrix. It will be recognized, of course, that the invention is not limited to this explanation for the improved bond obtained when a nickel coating is used, since other phenomena may also take place.

Any of a variety of steels may be employed in the bodies of the improved drag bit blades of the invention. In general it is preferred to utilize steels which have relatively low resistance to wear and abrasion. Specific examples of steels which are suitable for use in fabricating the blade bodies include those designated as A152 3310, A151 8620 and A151 2517. Other steels equally suitable will readily suggest themselves to those skilled in the'art. The blade body may be fabricated by machining it from a solid block of steel or may instead be formed by sintering powdered steel under heat and pressure in a suitable mold. Conventional sintering techniques may be employed.

The nickel coatingapplied to the steel blade body may be deposited by electroplating or by a hot metal spraying technique. Electroplating is generally preferred because it is less expensive, requires less equipment, and can be more readily controlled to produce a uniform deposit tree of pits and inclusions. Conventional electroplating equipment and solutions may be used. The thickness of the nickel coating may range from about 0.001 inch up to about 0.025 inch or more. A coating of from about 0.002 inch to about 0.010 inch is generally preferred.

The matrix metal used to infiltrate the chips or particles which serve as cutting elements in the blades of the invention should be capable of securely binding each of the individual chips in place and at the same time should be relatively tough and wear-resistant. The matrix metal will normally comprise one or more metals which melt at temperatures between about 1800" F. and about 2500 F. and have the ability to wet the cutting elements or chips when in the molten state. Metals melting above about 2500 F. are generally unsatisfactory because of the adverse effects of high infiltration temperatures upon the particles themselves. Suitable metals for use as the matrix include copper; copper-nickel alloys containing up to about 60 percent nickel; copperzinc alloys containing up to about 25 percent zinc; copper-nickel-zinc alloys containing up to about percent nickel and up to about percent Zinc; copper-silicon alloys containing up to about 3 percent silicon; coppersilver alloys containing up to about 80 percent silver; copper-beryllium alloys containing up to about 3 percent beryllium; copper-cadmium alloys containing up to about 18 percent cadmium; and similar alloys containing in addi tion small amounts, generally less than about 2 percent, of boron, iron, phosphorus, tin and the like. it will be understood that the above metals are merely representative of those which may beincluded in the matrix composition for bonding purposes and that other metals which melt at temperatures below those injurious to the particles used and will Wet the particles when in the molten state may be employed.

Wear-resistant properties may be conferred upon the matrix section of the finished blade by including a finelyd-ivided metal carbide with the abrasion-resistant chips to be infiltrated. Suitable carbides include cast or sintered tungsten carbide; titanium carbide; tantalum carbide; alloys of tungsten carbide with lesser amounts of tantalum carbide and titanium carbide; and tungsten, tantalum and titanium carbide alloys containing minor amounts of boron carbide, chromium carbide, vanadium carbide, molybdenum carbide, niobium carbide, and zirconium carbide.v The carbides utilized in this manner are employed in the form of fine powders, preferably ranging in size from about 150 mesh to about 400 mesh on the Tyler scale. ln order to promote Wetlability of these carbide powders by the molten matrix, a lesser amount of iron, nickel or cobalt is preferably utilized in conjunction with the carbide. It is preferred to employ from about 10 to about 25 percent iron, nickel or cobalt and to ball mill it with the carbide powder until the entire mixture has been thoroughly commingled and reduced to a 175 to 325 mesh size. The amount of iron, nickel or cobalt thus employed is independent of the quantity present in the carbide or boride composition employed.

The chips which are infiltrated with the matrix metal and serve as cutting elements in the drag bit blades of the invention may include any of a number of hard, abrasion-resistant materials having Rockwell A hardness values in excess of about 85. Suitable materials include diamond chips and particles of tungsten, titanium, tantalum, chromium, silicon, molybdenum, niobium, vanadium and zirconium boride or carbide. Boron carbide may also be used. The borides and carbides may be of the cast or cemented type, depending upon the manufacturing technique utilized. Cemented carbides, particularly tungsten carbide, generally contain from about 2 percent to about 25 percent by weight of iron, nickel or cobalt as the cementing agent or binder. Cobalt is most frequently used for this purpose. In general, cemented tungsten carbide and cemented mixed carbides consisting primarily of tungsten carbide and small additive amounts of tantalum carbide, titanium carbide, chromium carbide, vanadium carbide, or molybdenum carbide are preferred for purposes of the invention. These materials are generally considerably less expensive than diamonds and the metallic borides and in some cases are more effective. Suitable carbides are readily available from a number of commercial manufacturers.

The size of the chips employed as cutting elements in the blades of the invention is generally an important factor in determining the drilling rate and wear resistance of the blades. The chips should be small enough to prevent gross fractures and resultant rapid loss of major amounts of the matrix containing cutting elements and at the same time should be large enough to present a highly irregular cutting edge to the formation. This latter requirement dictates that the chips be appreciably larger than the basic grain size of the formation to be drilled. In general, the chips employed should fall within the range between about 0.045 inch and about 0.250 inch, as determined by means of screens having circular openings. When diamonds are employed as the cutting elements, sizes at the lower end of the scale will normally be used because of the high cost of large diamonds. it is preferred that the chips utilized be reasonably uniform in size, since too Wide a range in size may permit excessively close packing of the chips during fabrication of the blade and may result in improper bonding of the particles in the matrix.

These and other aspects of the invention can be more fully understood by referring to the following detailed description of the blades and the infiltration process for fabricating them and to the accompanying drawing, in which:

FIGURE 1 is a vertical elevation of a fixed blade drag bit provided with blades having a matrix containing tungsten carbide chips bonded to a nickel-plated steel blade body;

FIGURE 2 is a vertical elevation of the bit shown in FIGURE 1 rotated through an angle of FIGURE 3 is a bottom view of the bit shown in FlG- URES 1 and 2;

FEGURE 4 is a vertical elevation of a blade constructed in accordance with the invention for use in an extensible blade drag bit;

FIGURE 5 is a vertical elevation of the blade shown in FIGURE 4 rotated 90;

T-lGURE 6 is a cross-sectional view of the blade shown in FIGURES 4 and 5 taken along the line dfi in FIGURE 4;

FIGURE 7 is a schematic representation of the method utilized to fabricate drag bit blades in accordance with the invention;

FIGURE 8 is a photomicrograph showing the bond between a steel drag bit blade and a cupronickel matrix containing tungsten carbide chips;

FIGURE 9 is a photornicrograph showing the bond between a nickel-plated drag bit blade and a cupronickel matrix containing tungsten carbide chips; and,

FIGURE 10 is a photomicrograph showing the bond between a nickel-plated drag bit blade and a cupronickel matrix containing tungsten carbide chips.

Turning now to FIGURE 1 of the drawing, reference numeral 11 therein designates a generally cylindrical steel drag bit body containing an internal passageway 12, not shown in its entirety, through which drilling fluid may be circulated downwardly from the drill string to which the bit is connected during a drilling operation. Passageway 12 is provided with internal threads 13 to form a standard API tool joint box at the upper end of the bit. In some cases, the bit may instead be provided with external threads to form an API tool joint pin. Nozzles 14 are provided in the lower surface of the bit body in order to permit the discharge of drilling fluid from passageway 12 into the space beneath the bit during a drilling operation. Only one nozzle is shown in FIGURE 1 of the drawing but it will be understood that two or more nozzles will normally be provided. The nozzles may be lined with tungsten carbide or a similar material in the conventional manner in order to reduce erosion by the drilling fluid.

Blades 15 and 16 extend below the bit body in spaced relationship to the nozzles. The blades are welded to the bottom and sides of the bit body. As can be seen more clearly from FIGURES 2 and 3 of the drawing, the body is built up about the trailing surface of each blade during the welding operation in order to strengthen and better support the blade. The outer or gage edge of each blade is provided with an abrasion-resistant surface 17 of tungsten carbide or a similar material to reduce gage wear. This surface is normally formed at the time the basic blade structure is fabricated but in some cases may be applied later by conventional welding techniques. Diamonds 18 are embedded in abrasion-resistant surface 17 in order to further reduce gage wear. The diamonds are preferably about carat in size. They may be hand set after surface 17 has been formed by welding techniques or may instead be placed during fabrication of the basic blade structure, as will be pointed out more fully hereafter.

Each of the blades of the bit shown in FIGURE 1 of the drawing is provided with a matrix section 19 which extends across the face of the blade below the bit body. Chips of tungsten carbide or similar hard abrasion-resistant material which serve as the cutting elements of the blade are supported within the matrix. Since the upper part of the blade adjacent the body of the bit is used only for reaming and does no actual drilling, the matrix section need not extend upwardly over the entire length of the blade. It is preferred, however, to extend the matrix up the gage edge of the blade as shown in FIG- URE 1, leaving the blade bare adjacent to the body in order to facilitate welding it in place. The lower edge of each blade is tapered from an intermediate point upwardly to the inner edge in order to center the bit in the hole during the initial stages of the drilling operation. The blade will normally be tapered at an angle between about 15 degrees and about 45 degrees to the horizontal.

The construction of the blades shown in FIGURES 1 and 2 can best be seen from FIGURE 3 of the drawing. As shown in FIGURE 3, each blade includes a steel blade body 21. Prior to infiltration the body was electroplated with a coating of nickel about 0.010 inch thick on the face and gage surfaces, indicated by reference numeral 22. The nickel concentration in the matrix of the finished blade is therefore higher immediately adjacent these surfaces than elsewhere in the matrix. Although nickel is required only on the face and gage edge of the blade body, the entire body may be nickel plated if desired. Bonded to the face and gage edge of the steel body is matrix 23, a cupronickel bonding metal containing about Weight percent copper and about 25 weight percent nickel. Powdered tungsten carbide and nickel are dispersed within the matrix. Methods for forming the matrix will be discussed hereafter.

Sintered tungsten carbide chips 24, which serve as the cutting elements of the blade, are embedded in and supported by matrix 23. The chips range in size from about 0.10 to about 8.15 inch along their maximum dimension and are prepared by crushing larger pieces of tungsten carbide and screening the product. As shown in FIG- URE 3, the chips are arranged in two rows along the outer surface of the matrix and are spaced more closely together near the gage edge of the blade than at the inner edge. This provides greater abrasion resistance near the gage edge. In lieu of such an arrangement, chips uniformly spaced throughout a matrix which increases in thickness from the inner to the gage edge of the blade may be utilized. Tungsten carbide particles or chips are embedded in the matrix over the entire length of the gage edge of the blade in order to form abrasion-resistant surface I7 which serves to reduce gage wear. As pointed out earlier, the abrasionresistant surface may instead be formed by applying a coating of tungsten carbide to the gage edge by conventional welding techniques after the basic blade structure has been fabricated.

The drag bit blades of the invention may be employed with fixed blade drag bits of the type shown in FIGURES 1 through 3 of the drawing or may instead be utilized in conjunction with supported blade drag bits. Bits of the latter type differ from ordinary drag bits in that the blades employed are laterally supported adjacent their lower cutting edges by a movable section of the body of the bit. As blade wear occurs, this body section moves or is moved upwardly with respect to the blade so that the exposed blade length remains essentially constant. This permits the use of a much longer blade than would otherwise be feasible and therefore reduces the frequency with which trips must be made into and out of the borehole during a drilling operation. A supported blade drag bit with which blades fabricated in accordance with the invention may be used is disclosed in copending application Serial No. 832,539, filed in the name of Alexander B. Hildebrandt on August 10, 1959, now US. 3,066,749.

FIGURES 4, 5 and 6 of the drawings show a drag bit blade designed for use in conjunction with a supported blade drag bit. As can be seen from FIGURE 7, this particular blade embodiment includes an elongated steel blade body 1% provided with means at its upper end for detachably connecting the body to a supported blade drag bit. In this particular blade, the connecting means consists of a notch 101 in the blade which mates with a corresponding key or projection within the body of the bit. It will be understood, however, that this connecting means is not critical so far as blade performance is concerned and that the means used will depend upon the design features of the particular supported blade bit with which the blade is to be employew. The blade body, prior to infiltration, was provided with a nickel coating about 0.015 inch in thickness on the face and gage surfaces and hence the nickel content in the matrix of the finished blade adjacent to these surfaces is higher than elsewhere in the matrix. The entire surface of the steel blade body may be nickel coated prior to infiltration, although the presence of nickel is essential only on those surfaces to which the matrix is bonded. As in the earlier embodiment, it is preferred that the nickel coating be applied by an electroplating process. Matrix 102 containing aura is? tungsten carbide chips 103 is bonded to the blade body on the face and gage surfaces as shown in FIGURES and 6 of the drawing. In this embodiment of the invention, the matrix increases in thickness from the inner edge of the blade to the gage edge. The face and gage edge of the steel body are tapered to accommodate the matrix. The back of the blade is provided with a longitudinal spline 1.04 in order to stabilize it within the body of the supported blade bit for which the blade is intended. The designs of certain supported blade bits do not require that the blades to be used therein contain such splines. Again it will be recognized that the dimensions and configuration of the lade may be varied in order to permit its use in a variety of supported blade drag bits.

The matrix is composed of a cupronickel bonding metal containing about 75 weight percent copper and about 25 weight percent nickel. Dispersed within it is an abrasion resistant material made-up of about 82 percent tungsten carbide and about 18 percent nickel. The fabrication technique by means of which the matrix is formed will be described in detail hereafter. The tungsten carbide chips 103 uniformly distributed throughout the matrix are preferably chips of sintered tungsten carbide ranging in size from about 0.10 to about 0.15 inch along their maxir mum dimension. The chips on the gage edge of the blade provide a hard abrasion resistant surface which greatly reduces gage wear and extends the life of the blade. Diamonds 104 are embedded in the matrix along the gage edge in order to further reduce gage wear. The diamonds are about carat in size and as shown are arranged in a single row along the gage edge of the blade. The use of two rows or more of diamonds may be preferable in some instances.

The improved drag bit blades of the invention are fabricated by a casting or infiltration technique. This technique can best be understood by referring to Fl URE 7 of the drawing. in preparing the blades, a steel blade body containing a recess for the matrix section of the blade is first prepared by sintering powdered steel or by machining the body from a block of solid steel. A nickel coating is then applied to the recessed portion of the blade, or in some instances to the entire blade, by electroplating or by a hot metal spraying process. In either case, conventional techniques may be used. A carbon, ceramic, or other refractory mold containing a cavity conforming to the desired over all dimensions of the finished drag bit blade is prepared. Such a mold is indicated by reference numeral lit? in FIGURE 7 of the drawing. The steel blade previously prepared and coated with nickel is placed within the cavity in the mold with the recesses for the matrix section of the blade in an upward position. Diamonds, if they are to be utilized on the gage surfaces of the blade, are glued or otherwise afixed to the walls of the mold in the proper positions. The steel body in mold 110 is designated by reference numeral 111. Irregular chips or particles of tungsten carbide of suitable size, preferably between about 0.10 and 0.15 inch along their maximum diameter, which have been previously cleaned in alcohol, carbon tetrachloride or a similar solvent are placed in the voids in the blade body corresponding to the matrix section of the blade. A mixture of about 82 percent tungsten carbide powder and about 18 percent nickel powder which has been ball milled and screened to a 175-325 mesh size is poured into the mold voids around the tungsten carbide chips and gage diamonds. The mold may be vibrated to form a dense, evenly dispersed mass. The carbide Chips and powder are indicated by reference numeral 112 in FIGURE 7. Pellets of a cupronickel alloy containing about 75 weight percent copper and about 25 weight percent nickel are placed in a suitable crucible or other refractory vessel fitted with a conduit through which the alloy can flow into the mold and fill the spaces between the tungsten carbide chips and the powdered tungsten carbide-nickel mixture after the vessel and mold have been heated to ii an elevated temperature. refractory vessel is contained in the cover 113 of the mold. The alloy pellets are indicated by reference numeral 114. A small quantity of a borax flux is added to the alloy within the container. The mold containing the materials thus prepared is then placed in a furnace and heated to a temperature between about 2100 F. and about 2500 F, preferablyabout 2250 F. The mold is held at this temperature for the period of from about 5 to 20 minutes. As the metal alloy bonding material in the receptacle in the mold cover melts, it flows through the passageway in the cover into the voids in the mold and results in bonding between the nickel plated steel blade, the tungsten carbide nickel powder, the tungsten carbide chips, and the gage diamonds. At the end of about 5 to 20 minutes, the mold is taken out of the furnace and cooled. The blade may then be removed from the mold. It may be heat treated by conventional means to alter the steel hardness and remove thermal stresses. irregularities in the blade surface may be removed by grinding or machining if desired. The finished blade thus prepared may be welded to the body of the drag bit in the conventional manner or may be utilized in a supported blade type drag bit, depending upon the design features of the blade.

It will be understood that the drag bit blades and the blade fabrication technique described in conjunction with the drawing are directed to specific blades constructed in accordance with the invention and that all the limitations recited with respect to those particular blades are not necessarily limitations applicable to all blades falling within the scope of the invention. The blades of the invention may be constructed of either cast or sintered steel and may utilize a variety of matrix materials and cutting elements. The application of a nickel coating to the steel body prior to infiltration improves the bonding between steel and a variety of matrix metals. The improved blades of the invention may be utilized in conjunction with drag bits having two, three, four or more blades and are applicable to both core bits and full hole dragbits. These and similar modifications to the specific bits described abovewill vbe readily apparent to those skilled in the art.

The benefits derived by coating a steel or similar ferroalloy surface with nickel prior to the application of a matrix containing metal carbide to it by infiltration can be readily seen by considering the results obtained with a series of drag bit blades in laboratory and field tests. Thefirst set of blades tested wasprepared by bonding a matrix composed of about weightpercent copper and about 25 weight percent nickel to A181 3310 steel blade bodies by infiltration. Tungsten carbide chips ranging between about 0.1 and about 0.15 inch were packed into voids adjacent the leading and gage surfaces of the body in a refractory mold. A -300 mesh powdered mixture of about 82 percent tungsten carbide and about 18 percent nickel was poured into the mold to fill the spaces around the chips. The structure thus prepared was then infiltrated with the molten matrix metal at a temperature of about 2350 F. in the manner described heretofore. After the mold had cooled, the blades were removed and welded to a 6% inch drag bit body. This bit was then tested in an oil field drilling operation. It was found that the blades failed prematurely due to fracturing of the matrix where it was bonded to the steel. Large pieces of the matrix were lost from the faces of the blades near the gage edge, rendering them useless. Subsequent metallographic examination of the blades showed a disconnected series of small voids in the matrix extending parallel to the steel about 0.002 inch from the undisturbed steel surface. FIGURE 8 in the drawing is a photomicrograph of a section of one of these blades. The voids are clearly visible.

Following the above tests, a second set of blades prcparcd. rhese were similar to tiose described above As shownin FIGURE- 7, the.

except that the blade bodies were copper plated prior to application of the matrix by infiltration. Metallographic examination again showed the existence of voids near the bond between the matrix and steel. FIGURE 9 is a photomicrograph showing these voids. Even though the copper coating may have protected the steel against oxidation during infiltration, the copper itself was apparently suificiently oxidized to permit generation of carbon monoxide or carbon dioxide and the formation of voids.

A third set of blades was then prepared in accordance with the invention by electroplating steel blade bodies with nickel and thereafter bonding a copper-nickel to the bodies by infiltrating tungsten carbide chips and tungsten carbide-nickel powder in a mold as earlier described. FIGURE is a photomicrograph of the juncture between the steel and matrix. It will be noted that the matrix, unlike that in the earlier blades, was essentially free of voids. The resistance of nickel to oxidation at elevated temperatures is considerably higher than that of steel, copper, copper-nickel alloys and tie like.

It is believed that this resistance to oxidation and the wetting properties of the nickel were responsible for the better bonding. Field tests of this bit revealed no noticeable tendency toward fracturing and resultant loss of the matrix under high shearing stresses across the bond.

Although the invention has been described largely in terms of fabricating drag bit blades, it will be apparent that good bonding is necessary in many other instances where a matrix containing a metal carbide must be applied to a steel or other ferroalloy surface. The abrasion resistance of the carbide permits the use of such a matrix in a variety of applications, particularly if finely-divided metal carbide is used in place of the chips which serve as cutting elements in the drag bit blades. Shovels, mills, scrapers, stirrers and similar equipment are often hard surfaced to reduce wear. Nickel plating the ferroalloy surfaces to which a matrix containing metal carbide is to be applied on such equipment by infiltration will result in better bonding and less likelihood of failure under high stress. The method of the invention is therefore not to be limited to the fabrication of drag bit blades and instead may have Wide application out-side the drag bit field.

What is claimed is:

1. A method for increasing the abrasion-resistance of a ferroalloy tool which comprises coating the surface of said tool with nickel, placing abrasion-resistant particles having a Rockwell A hardness in excess of about 85 in contact with the nickel-plated surface of said tool in a refractory mold, heating said mold and its contents to a temperature in the range between about 2100 F. and about 2500 F., infiltrating said particles in said mold with a molten matrix metal melting between about 1800 F. and about 2500 F. and having the ability to wet said abrasion resistant particles and nickel-coated surrace, allowing said mold to cool, and thereafter removing said tool from said mold.

2. A method as defined by claim 1 wherein said tool is electroplated with nickel.

3. A method as defined by claim 1 wherein said abrasion-resistant particles are metal carbide particles.

4. A method for fabricating an improved drag bit blade which comprises nickel plating the front and gage sur-, faces of a steel blade body with a coating of nickel from about to about 0.025 inch thick; placing metal carbide particles having a Rockwell A hardness in excess of about in contact with the nickel-plated front and gage surfaces of said blade in a refractory mold, said particles ranging size between about 0.045 and about 0.250 inch; placing a mixture of powdered metal carbide and powde eo'. nickel in the interstices between said particles in said mold; heating said mold and its contents to a temperature in the range between about 2100 F. and about 2500" infiltrating the particles and powder in said mold with a molten copper alloy matrix metal melting between about 1800 F. and about 2500 F. and having the ability to wet said particles, said powder and said nickel-plated surfaces; allowing said mold to cool; and thereafter removing the blade from said mold.

5. A method as defined by claim 4 wherein said metal carbide particles are cemented tungsten carbide particles containing cobalt as a binder.

6. A method as defined by claim 4 wherein said matrix metal is a copper-nickel alloy containing less than about 60 percent nickel.

7. A method as defined by claim 4 wherein said metal carbide particles range between about 0.1 and about 0.15 inch in size.

References Cited by the Examiner UNITED STATES PATENTS 1,847,302 3/32 Emmons 77-70 1,855,330 4/32 Zublin 76-108 1,923,488 8/33 Howard et al -410 2,057,209 10/36 Schlumpf 76-108 2,337,322 12/43 Gascoigne 76-108 2,511,991 6/50 Nussbaum 175-330 2,712,988 '7/55 Kurtz 51-309 2,973,047 2/61 Edgar et a1 76-108 X 2,978,846 4/61 Barron 51-206 GRANVILLE Y. CUSTER, JR., Primary Examiner.

BENEAMIN BENDETT, FRANK H. BRONAUGH, Examiners. 

1. A METHOD FOR INCREASING THE ABRASION-RESISTANCE OF A FERROALLOY TOOL WHICH COMPRISES COATING SURFACE OF SAID TOOL WITH NICKEL, PLACING ABRASION-RESISTANT PARTICLES HAVING A ROCKWALL A HARDNESS IN EXCESS OF ABOUT 85 IN CONTACT WITH THE NICKEL-PLATED SURFACE OF SAID TOOL IN A REFRACTORY MOLD, HEATING SAID MOLD AND ITS CONTENTS TO A TEMPERATURE IN THE RANGE BETWEEN ABOUT 2100* F. AND ABOUT 2500* F., INFILTRATING SAID PARTICLES IN SAID MOLD WITH A MOLTEN 